Fe–Mn Binary Oxide Impregnated Chitosan Bead And Its Arsenic And Phosphate Adsorption Properties

Arsenic is a metalloid element with high toxicity. With the wreathing of rocks and human activities, it enters into the aquatic environment, causing the pollution of groundwater and surface water. The arsenic concentrations of groundwater in many contraries and regions are at high levels, posing a huge threat to human health. Phosphorus is a necessary nutrient element for biological growth. However, the high content of phosphorus often leads to eutrophication of water body, which influencesser iously the water quality and ecosystem health. There are several common techniques for arsenic and phosphate removal from water. Among them, adsorption is one of the most promising methods. Generally, the majority of adsorbents prepared are powder, which limits their application in real water treatment. Therefore, the granulation of powdered adsorbents becomes very important and has gained increasing attention.Previous results show that powdered Fe-Mn binary oxide is highly effective for arsenic and phosphate from water. As a non-toxic and biodegradable polymer, chitosan is a good binder and can be used to embed powders as a matrix. In this study, a novel Fe-Mn binary oxide impregnated chitosan beads adsorbent was prepared. The as-prepared adsorbent was systemically characterized using different techniques and its performance in arsenic and phosphate removal was investigated in detail. The main results are as following:1. The prepared Fe–Mn binary oxide impregnated chitosan bead（FMCB） has good mechanical strength（1.5².5 N） and a larger specific surface area of 248.2 m²·g^-1, with a grain diameter of 1.6¹.8 mm.2. The FMCB inherited the high arsenic adsorption ability of the powdered Fe–Mn binary oxide. At pH 7.0±0.1, the maximal adsorption capacities are 54.2 mg·g^-1 and 39.1 mg·g^-1 for As（III） and As（V）, respectively. The bead is effective for arsenic removal in a wide pH range of 5.0¹0.0. The co-existing Ca2+and Mg2+ enhanced slightly the arsenic adsorption. The present HCO3- and SO42- had little effect on arsenic adsorption. However, the SiO32- and PO43- hindered the arsenic removal.3. The FMCB has good adsorption performance towards phosphate. The maximal adsorption capacity is 13.3 mg·g^-1 at pH 7.0±0.1. In a wide pH range of 5.0¹0.0, the adsorbent is effective for phosphate adsorption. The co-existing Ca2+ and Mg2+ enhanced slightly the phosphate adsorption. The present HCO3-, SO42- and Cl-1 had no significant influence on phosphate adsorption. However, the SiO32- inhibited the phosphate adsorption.4. The dried FMCB can be easily used in the flow-through system. The experimental results of column tests demonstrated that about 1500 and 3200 bed volumes of simulated groundwater containing 233 μg·L^-1 As（V） and As（III） were respectively treated before breakthrough(10 μg·L^-1). For the simulated wastewater containing 3mg·L^-1 phosphate, about 800 bed volumes was treated when the phosphate concentration in effluent reached the limit of 0.5 mg·L^-1.5. The FMCB is well regeneratable and the adsorbed arsenic and phosphate can be desorbed with NaOH solution. It can be used repeatedly.Generally, the Fe–Mn binary oxide impregnated chitosan bead is a promising adsorbent for arsenic and phosphate removal, due to its good mechanical strength, high adsorption capacities and reusability.